The objective of this application is to investigate the association of use of antioxidant-containing dietary supplements with DMA damage and repair. This is an important area of research because 100 million Americans use dietary supplements despite the lack of definitive evidence for benefit or harm, with the exception of known adverse effects of B-carotene in smokers. We are particularly interested in the influence of dietary supplements on DNA damage and repair (known to be associated with cancer risk) since such damage can be mitigated by nutritional factors, especially antioxidants. Because the nutrient dose from supplements is often 10 to 100 times the dose available from a balanced diet, the nature and magnitude of the associations of antioxidant dose with DNA damage and repair capacity may be different for high-dose supplement users, compared to non-users. These questions have not been previously examined in epidemiologic investigations. We hypothesize that use of antioxidant-containing dietary supplements (vitamin C, vitamin E, B-carotene and selenium) is associated with low levels of DNA damage and high DNA repair capacity. We also hypothesize that use of prooxidant supplements (iron) is associated with high levels of DNA damage and low DNA repair capacity. To test these hypotheses, we will use single cell gel electrophoresis (the comet assay) to measure DNA damage and repair capacity in peripheral blood specimens of 220 healthy adults aged 50-74 years who are participants in A Cohort Study of Dietary Supplements and Cancer Risk (R01 CA74846). The following data are collected and analyzed and will provide antioxidant exposure information: dietary supplement use measured from a home visit inventory; usual diet from a food frequency questionnaire; and biomarker based measures of serum vitamin E (a and y tocopherol), vitamin C and carotenoids and toenail selenium. The outcome, DNA damage and repair, will be measured as part of this study in archived peripheral blood specimens using the comet assay. The comet assay is a rapid, economical and reliable assay that measures DNA damage and repair in individual cells. This assay is very well suited for use in epidemiologic investigations. Our study design will facilitate the ability to investigate multiple types of supplements, dose-response effects for a given supplement, combinations of several supplements and interactions of antioxidants from supplements with antioxidants from food in relation to DNA damage and repair. [unreadable] [unreadable] [unreadable]